The present invention relates to an improvement of a method of so called automatic band saw cutting and a machine for practicing the method, in which a desired mechanical cutting of a metallic or nonmetallic workpiece is performed by gradually lowering an endless belt-like flexible band saw made of steel and the like, bridging two pulleys and rolling around said pulleys, while forcing said band saw to carry out a continuous forced-circulation running.
An outline of a conventional machine for cutting by a band saw is shown in FIG. 1, in which a band saw 3, bridging two pulleys 1 and 2 and rolling around said pulleys in a form of an endless belt is made to perform continuously forced-circulation running by a motor for machining connected to one of said pulleys and to descend to cut a workpiece placed under the band saw 3. Therefore, according to this method, machining tracks of the machining groove of the workpiece A are linear. According to this conventional method, the length of machining of the workpiece A by the band saw 3, namely tne width of machining l equals to the width L of the workpiece A, and when this width is relatively great, chips generated in the machining groove as the machining motions goes on accumulate between each tooth of the saw until a state of so called loading that will impede normal machining motions is presented. The greater the width of machining l of the workpiece A is, and the poorer the machinability of the material of the workpiece is, for example, stainless steel, more easily loading is generated. This loading increases machining resistance and not only shearing heat is produced to lower in the machining efficiency but also the life of the saw is shortened, which will cause the impossibility of machining. Therefore, according to the conventional method, a motor of a large size is used to run the band saw taking in consideration of lowering in the efficiency of the machine due to generation of loading. At the same time, it has been required to reduce the machining speed to a great extent for alleviating generation of loading, which means that its mechanical efficiency and working efficiency are very low besides of the necessity of restricting the size of the workpiece A.